Duct electrical heater unit

ABSTRACT

An electrical resistance heater module or unit for insertion into ductwork, said unit having electrical resistance elements supported in a frame the side members of which have locator means in the nature of interfitting shoulders providing lateral and normal stops which allows the individual units to be positioned in side by side relation in a registered manner and easily assembled into a composite heater of the desired heating capacity, or disassembled therefrom for ease of repair or replacement of separate units or the resistance elements thereof.

United States Patent 1191 McBride et al.

[111 3,811,031 [451 May 14, 1974 DUCT ELECTRICAL HEATER UNIT [75] Inventors: Roby C. McBride, Limestone;

Howard Owens, Jonesboro, both of Tenn.

[73] Assignee: TPI Corporation, Johnson City,

Tenn.

22 Filed: Jan. 29, 1973 [21] Appl. No.: 327,581

[52] US. C1..,. 219/374, 219/375, 219/381,

219/532, 338/290, 338/305, 338/317, 338/321 [51] Int. Cl. H05b 3/06 [58] Field of Search 219/374, 375, 376, 381,

[56] References Cited UNITED STATES PATENTS 3,697,923 10/1972 Griffes 338/318 X 3,368,617 2/1968 Rosman et al. 165/175 1,307,198 6/1919 Harth 219/546 X 3,098,145 7/1963 Raymond 219/374 X 3,102,185 8/1963 Boyd et ul..... 219/374 X 3,116,394 12/1963 Burton 219/382 3,472,316 10/1969 Couch, Jr. 165/149 X Primary Examiner J. V. Truhe [57] ABSTRACT An electrical resistance heater module or unit for insertion into ductwork, said unit having electrical resistance elements supported in a frame the side members of which have locator means in the nature of interfitting shoulders providing lateral and normal stops which allows the individual units to be positioned in side by side relation in a registered manner and easily assembled into a composite heater of the desired heating capacity, or disassembled therefrom for ease of repair or replacement of separate units or the resistance elements thereof.

7 Claims, 12 Drawing Figures PATENTEBNAY 14 um SHE! 2 0F 2 DUCT ELECTRICAL HEATER UNIT The present invention relates to improvements in electrical resistance heaters, variously termed open wide range of desired heating capacities. Such compos-' ite heaters find particular application installed in the sheet metal heating ducts of homes or other buildings.

In the electrical heating art, particularly concerning duct heaters, it is common practice to manufacture the entire or composite heater as a single unit to the re quired heating capacity and exterior structural dimensions for a particular job. In practice, the electrical resistance elements, conventionally comprised, for example, of exposed or sheathed nickel-chrome resistance wires which may be coiled, are supported'in the bank such as shown, for example, in US Pat. No. 3,102,185, and positioned in the duct such that the air flow is around and in close proximity to the exposed or electrically insulated resistance wire. Where a single bank does not give the required heat output, two or more such banks are supported within a common frame.

Heretofore, thesemultiple bank heaters have been constructed more or less as a permanently unitary structure with noconvenient provision made for replacement of a defective or burned out resistance element. Oftimes, in fact, the sheet metal housing for a plurality of heater banks is actually welded together, making replacement of the resistance elements an onerous, if not impossible, task. Such unitary construction, employing several banks, also makes assembly somewhat tedious anddoes not lend itself'readily to rapid and machine oriented fabrication.

Objects, therefore, of the present invention are: to provide an electrical resistance heating unit which may be, manufactured in one or more standard sizes and assembled into a multi-unit composite heater of any desired capacity; to provide such heating unit with structure which willallow rapid and precise assembly into or disassemblyfrom said composite.

These and other objects hereinafter appearing have been attained in accordance with the present invention through novel construction hereinafter described in detail, including the provision on frame members ofa single heater unit, of novel locator means which allow rapid positioning and interconnection of the heater units with respect to each other in order to assemble a composite heater of the desired heating capacity and size.

The heating unit of the present invention may be structurally defined as comprising a pair of spaced, elongated frame members, each of which comprises a longitudinally extending web bordered on each of its longitudinal edges with locator means, each of said locator means comprising a lateral stop and a normal stop, said stops being interconnected with each other and said web, a plurality of resistance element racks extending between and connectedto said frame members tance elements positioned in said supports and provided with terminals for electrical connection to a Power Source.

at their webs, said racks being spaced apart and pro- A more comprehensive understanding of the present invention may be had from the following description and drawings wherein:

FIG. 1 is a side view of a composite heater of the present invention mounted in a heating duct, with the duct and control box in cross-section and portions of the frame members broken away to show detail;

FIG. 2 is a front view of the composite heater of FIG. 1 taken along the line 2-2 thereof in the direction of the arrows;

FIG. 3 is an end view, enlarged, of a frame member of a heater unit of FIG. 2 in the direction of the arrow FlGS. 4-9 are end view variations of the configuration of the frame member of FIG. 3;

FIG. 10 is a cross-sectional view through the resistance element racks of two of the heater units of FIG.

1 taken along line 10-10 thereof in the direction of Referring to the drawings, particularly to FIGS. 1-3, an electric heater generally designated 13 embodying the present invention is shown mounted in a heating duct 14. The duct and heater are depicted as rectangular with their long transverse axes horizontal, however, they may, of course, be of any convenient configuration including square or having their long transverse axes verticle. The duct is conventionally sheet metal and is shown for purposes of clarity of a greater thickness than is generally employed.

The heater 13 according to the present invention is usually, but not limited to, a composite of a plurality of individual heater units comprising a pair of frame members l6, hereinafter described in detail, heating element racks 18 extending therebetween, and heating elements 20 strung through the racks. An adjunct to the composite heater 13 is a control box 22, which, in the drawing, is shown to provide a convenient mount for the heater.

The view of the composite heater in HO. 1 shows, for the most part, a side view of a single heating unit, the other units being positioned in back of it, however,

FIG. 2 shows a series of six of the units generally designated 23, assembled and secured together by means of rear tie members 24 and front tiemembers 26. The shape and structure of these tie members is unimportant except as hereinafter specifically indicated.

Referring further to FIGS. 1-3, the resistance elements 20 are conventionally, but not limited to, coiled resistance wire having a coiled spring-like configuration and having a general U shape with its ends or terminals 28 threaded or provided with other suitable means for attachment to the control box 22 and a power supply. The terminals 28 may be welded or otherwise secured as by mechanical clamping to the coiled wire. Terminals 28 are shown passing through an insulating grommet 30 fixedin the rear wall 32 of the control box 22 and locked in position by nuts 34. The configuration, of course, of grommets 30 and the locking means 34, can be varied widely according to well known structure in the art. Control box 22 may contain the electrical components usually associated with control means for duct heaters, such as thermal cut-out switches, on and off automatic switches, fuses, transformers, thermostat connection, and the like. The terminals 28 may be connected to suitable conduits for connection to a remotely located control box or other control means. In such an arrangement, wall 32 may be unassociated with the control box. The resistance elements may be of any size and current carrying capacity. Typically, these elements may accommodate a wide range of electrical parameters, such as, for example, 120-600 volts, l-l,000 amps, and operating temperatures'of up to l,000 F. or more.

In the arrangement shown in FIG. l3, an opening 35 is cut in a section of the duct 14 and provides edge portions 36, 38, 40 and 42. The heater l3, conveniently attached through front tie members 26 to wall 32 by screws 44, is inserted through this opening and supportedin the position shown by a plurality of screws or the like 46 securing wall 32 to the aforesaid edge portions 36, 38, 40 and 42 forming the duct opening. In actual use of large composite heaters, it is often advisable to provide one or more feet 43 on the rear of the heater, such as on rear tie member 24 to take the strain off the rear wall 32 of the control box and also to minimize vibratory motion of the composite heater. A sealing gasket 48 is preferably provided between the duct and wall 32 to seal against air, moisture, dust or the like. Control box 22, as shown, may be provided with a hinged outer wall 50 and snap catch 52 for easy access to the terminals 28 and screws 46.

Other suitable arrangements for mounting heater 13 in the duct are, of course, evident, such as providing on the top and bottom of the duct flanges extending upwardly arid downwardly therefrom adjacent opening 35, and extending wall 32 of the control box to above and below the duct to engage the said flanges for attachment thereto in any suitable manner. The manner of removably attaching the control box, or wall 32 to the duct is not of importance to the present invention in the sense of limiting the scope thereof.

The particular configuration of a preferred form of the frame members 16 is seen in FIG. 2 where portions of the front tie members 26 are broken away to expose an end view of the frame members of the heating units 23 and a portion of the rear tie members 24 which help to support the individual units 23 in their series arrangement. Thisend view is shown in FIG. 3 in partial enlargement for purpose of clarity. It is noted that frame members 16 are shown as being of the same cross-sectional configuration, however, it will become apparent from FIGS. 49 that variations may be employed.

Referring to FIG. 3, the frame member generally designated 16 may be formed conveniently from a single piece of sheet metal by rolling or stamping to provide a longitudinally extending web' 54 bordered on its longitudinal edges with locator means comprising lateral stops 56 and 58 and normal stops 60 and 62. The term lateral refers to a direction generally in the plane of web 54 and across the longitudinal axis of the frame member, while the term normal" refers to a direction generally perpendicular to the plane of web 54. It is apparent, however, that these frame members may be fabricated from two or more sheet metal pieces secured together by rivets or the like. In the embodiment shown in FIG. 3, normal stop 60 is approximately the same distance from web 54 as normal stop 62 in order that all of the webs 54 of the frame members lie approximately in the same plane when the frame members are secured together in series arrangement. This construction allows for contact of the tie members 24 and 26 with all of the webs as shown in FIG. 2. The tie members are conveniently secured to the rear and front ends of the frame members at their webs by sheet metal screws 64.

Referring to FIG. 4, lateral stop 56 is provided by means of the outer edge of the longitudinal shoulder which forms normal stop 60. In FIG. 5, the lateral stops 56 are shown as immediately adjacent the outer plane of web 54, but, normal thereto. In FIG. 6, alternate frame members such as the middle one shown in this figure are provided with shorter normal shoulders than their abutting neighbors. This construction still allows all of the webs 54 to lie in the same plane. In FIG. 7, the frame members are the same size and the nonplanar posture of adjacent webs 54 is apparent. Such structure is not preferred, but, where the sheet metal of the frame members is light gauge, it is apparent that the nonplanar posture approaches a negligible factor. In FIGS. 8 and 9, the basically U shaped configuration of longitudinally extending shoulders which provide the lateral and normal stops provides an interlocking structure in both a lateral and a normal direction.

One embodiment of the resistance element rack generally designated 18 is shown in FIGS. 10-12. The rack 18 is conveniently formed from sheet metal and is provided with substantially flat body portions 66 and 68, strengthening ribs 70, strengthening flanges 72, and support legs 74. Each rack is further formed with a plurality of apertures 76 to each receive an insulating grommet 78 or similar type insulator having a bore 80 through which the resistance elements 20 are strung. One side 82 of a peripheral flange 84 on the grommet bears against the edges of the rack body portion forming aperture 76 and is locked to the rack by means of tabs 86 bent against the other side 88 of flange 84. The

configurations of the racks l8, grommets 78 and resistance elements as shown are not intended to limit the present invention, as it is apparent to those skilled in the art that many other equivalent structures and configurations could be employed.

Referring to FIG. 10, the racks, shown in crosssection, are attached to the webs 54 of the frame members 16 through support legs 74, at the points, for example, 90 by means of spot welding or mechanical fasteners such as screws or rivets. Where screws or rivets are employed, it is preferable to countersink them to the level of the outer surface of the web in order to clear the rear tie members 24 for reasons hereinafter discussed.

Referring to the variations in cross-sectional configurations of the frame members 16 as shown in FIGS. 3-9, it is particularly pointed out that each embodiment has a longitudinal web 54 and locator means comprising lateral stops 56 and 58 and normal stops 60 and 62. It is within the purview of one skilled in the art to devise many other shapes andconfigurations for the frame members, however, the combination of the lateral and normal stops are needed in order to obtain the full advantages of applicants invention. In FIGS. 8 and 9, the cross-sectional configuration provides a key type lateral motion interlock for the assembled heating units.

In the use of the present invention it is seen that removal of the two pairs of screws 64 from the webs of the upper and lower frame members (see FIG. 1), and removal of nuts 34 from the terminals of the associated unit 23, allows the unit to be slid out of the composite heater for repair or replacement of, for example, any of its resistance elements 20. The control box would first be unscrewed from the duct and the composite heater and control box removed from the duct. The locator means insures proper placement of the units with respect to each other and to and the control box and allows rapid assembly of the unitsinto the composite heater and removal therefrom.

Although the invention has been described in considerable detail with particular reference to certain preferred embodiments thereof, variations and modifications can be effected without departing from the spirit and scope of the invention.

We claim:

1. An electrical resistance heating unit comprising a pair of spaced, elongated frame members, each of which comprises a longitudinally extending web bordered on each of its longitudinal edges with locator means, each of said locator means comprising a lateral stop and a normal stop, said stops being interconnected with each other and said web, and lying to one side of the plane of said web, a plurality of resistance element racks extending between said connected to said frame members at their webs on the aforesaid one side of said plane, said racks being spaced apart and provided with electrically insulative grommets secured in apertures in said racks, and resistance elements positioned in and passing through said grommets and provided with terminals for electrical connection to a power source.

2. The heating unit of claim I wherein said web and locator means comprise a unitary, sheet metal structure.

3. A plurality of heating units of claim 1 serially connected together with lateral and normal stops of each unit positioned respectively adjacent lateral and normal stops of the unit adjacent thereto, such that the webs of the adjacent frame members lie substantially in a common plane.

4. The heating unit of claim 1 wherein each of said locator means is provided with a plurality of laterally spaced lateral stops to provide a key type lateral motion interlock for a serially assembled plurality of said units.

5. An electric blast coil duct heater unit comprising a pair of spaced, elongated frame members each formed to provide a substantially flat rectangular web having a longitudinal and a transverse axis, longitudi' nally extending first shoulder means adjacent each longitudinal edge of said web, each of said shoulder means extending generally in the same normal direction from the plane of said web to provide a lateral stop to each edge of said web, longitudinally extending second shoulder means extending outwardly from each of said first shoulder means in a generally normal direction thereto to provide a normal stop to each edge of said web, a plurality of resistance element racks extending between and connected to saidframe members at one side of their webs such that the other side of said webs lie outwardly from the first and second shoulder means associated therewith, said racks being spaced apart and provided with electrically insulative grommets secured in apertures in said racks, and resistance elements positioned in and passing through said grommets and provided with terminals for electrical connection to a power source.

6. A plurality of heating units of claim 5 serially connected together with lateral and normal stops of each unit positioned respectively adjacent lateral and normal stops of the unit adjacent thereto, such that the webs of the adjacent frame members lie substantially in a common plane.

7. The heater unit assembly of claim 4 attached to a wall member, said wall member being attached to wall portions ofa heater duct, said wall portions defining an opening through a side of said heater duct through which said assembly projects into said heater duct. 

1. An electrical resistance heating unit comprising a pair of spaced, elongated frame members, each of which comprises a longitudinally extending web bordered on each of its longitudinal edges with locator means, each of said locator means comprising a lateral stop and a normal stop, said stops being interconnected with each other and said web, and lying to one side of the plane of said web, a plurality of resistance element racks extending between said connected to said frame members at their webs on the aforesaid one side of said plane, said racks being spaced apart and provided with electrically insulative grommets secured in apertures in said racks, and resistance elements positioned in and passing through said grommets and provided with terminals for electrical connection to a power source.
 2. The heating unit of claim 1 wherein said web and locator means comprise a unitary, sheet metal structure.
 3. A plurality of heating units of claim 1 serially connected together with lateral and normal stops of each unit positioned respectively adjacent lateral and normal stops of the unit adjacent thereto, such that the webs of the adjacent frame members lie substantially in a common plane.
 4. The heating unit of claim 1 wherein each of said locator means is provided with a plurality of laterally spaced lateral stops to provide a key type lateral motion interlock for a serially assembled plurality of said units.
 5. An electric blast coil duct heater unit comprising a pair of spaced, elongated frame members each formed to provide a substantially flat rectangular web having a longitudinal and a transverse axis, longitudinally extending first shoulder means adjacent each longitudinal edge of said web, each of said shoulder means extending generally in the same normal direction from the plane of said web to provide a lateral stop to each edge of said web, longitudinally extending second shoulder means extending outwardly from each of said first shoulder means in a generally normal direction thereto to provide a normal stop to each edge of said web, a plurality of resistance element racks extending between and connected to said frame members at one side of their webs such that the other side of said webs lie outwardly from the first and second shoulder means associated therewith, said racks being spaced apart and provided with electrically insulative grommets secured in apertures in said racks, and resistance elements positioned in and passing through said grommets and provided with terminals for electrical connection to a power source.
 6. A plurality of heating units of claim 5 serially connected together with lateral and normal stops of each unit positioned respectively adjacent lateral and normal stops of the unit adjacent thereto, such that the webs of the adjacent frame members lie substantially in a common plane.
 7. The heater unit assembly of claim 4 attached to a wall member, said wall member being attached to wall portions of a heater duct, said wall portions defining an opening through a side of said heater duct through which said assembly projects into said heater duct. 